Notes on the Microstructure of the Nautilus Shell

The shell of the Nautilus was examined using scanning electron microscopy, transmission electron microscopy and polarized light microscopy. The structure consisted of two major layers: a porcellaneous outer layer and a nacreous inner layer. Most of the porcellaneous layer was composed of granular crystals randomly distributed with a substructure suggestive of bundles of acicular crystallites. A separate prismatic sublayer of the porcellaneous material was composed of a more regular arrangement of crystals. The nacre was composed of alternating crystalline lamellae and films of organic material. The lamellae were formed of many polygonal crystal platelets. The growth surface of the nacre consisted mainly of stacks or towers of incomplete platelets but some areas showed a terraced form of growth in which each crystal lamella was essentially completed before the next covered it. The porcellaneous material, which is exposed to the external environment, and thus requires a greater erosion resistance, was considerably harder than the nacre. It was found that the internal shell walls showed further layers of material not present in the outermost whorl. These were a thin organic layer, which appeared as a boundary between the existing and added material, and a thick layer of nacre. This extra nacre may be useful in the shell\u27s buoyancy control. The siphunclar tube, examined with scanning electron microscopy and polarized light microscopy, appeared in cross-section as a ring of semi-prismatic crystals outside a dark organic hoop. A bisection of the septal neck showed that this ring fits like a sleeve over the nacre of the septal neck

Ultrastructural Observations of the Argonaut Shell

An examination of the ultrastructure of the shell of the cephalopod Argonauta Nodosa was carried out using scanning electron microscopy, transmission electron microscopy and polarised light microscopy. The structure of the Argonaut shell was found to consist of an inner and outer prismatic layer separated by a thin central zone which was sparsely occupied by spherulitic crystals. Fluctuations in the width and porosity of the central zone resulted in changes in the shell\u27s opacity and gave rise to the fibrous lines visible in the structure. The central zone was the region of initial growth and was the nucleating point for the crystals which formed the prismatic layers. It was concluded that deposition of material in the Argonaut shell occurred on both the inner and outer surfaces of the shell, in contrast to the single growth surface of other molluscs. The deposition process can be explained by the periodic movement of the Argonaut\u27s tentacles, which are responsible for the material secretion, from one surface to the other. In general it was found that the Argonaut exercises Jess control over the structure of its shell than is common amongst the molluscs and in particular the organic matrix of the shell does not appear to play as large a role in determining the crystal structures

The Effect on the Ultrastructure of Dental Enamel of Excimer-Dye, Argon-Ion and CO2 Lasers

This study aimed to investigate the ultrastructural changes that occur in dental enamel irradiated with pulsed excimer-dye, continuous-wave (CW) argon-ion and CW CO2 lasers. The pulsed excimer-dye laser produced deep craters, rough damaged surfaces with underlying porosity and amorphous vitrified material. The vitrification of the enamel indicated that the temperature in these areas must have been al least in the range 1280 to 1600°C. The CW argon-ion laser irradiation produced a changed non-cratered surface with inter-crystalline porosity and a mixture of small and some large irregularly packed recrystallized enamel crystals. The CW CO2 laser produced shallow craters, surface crazing and lifting off and removal of the surface layer to expose the underlying roughened enamel. T he ultrastructure revealed inter-and intra-crystalline porosity, a mixture of small but variable size irregularly packed recrystallized enamel crystals and also well packed large crystals which indicated further grain growth. The porosity in lased enamel was overall very similar to that seen in enamel heated in an electric furnace to a temperature of 600°C. The presence of recrystallized enamel crystals indicated a temperature rise of ~1000°C and the grain growth indicated that a temperature 2: 1000°C existed for some time after the laser irradiation. In general the excimer-dye laser produced most surface destruction because of its higher power density and shorter interaction time and the argon-ion laser produced least damage. These results indicated that the lasers used in this study require much more refinement before they can find therapeutic application to dental enamel, and this may well be the case for other lasers being investigated for clinical dental practise

Glaucoma spectrum and age-related prevalence of individuals with FOXC1 and PITX2 variants

Published online 3 May 2017Variation in FOXC1 and PITX2 is associated with Axenfeld-Rieger syndrome, characterised by structural defects of the anterior chamber of the eye and a range of systemic features. Approximately half of all affected individuals will develop glaucoma, but the age at diagnosis and the phenotypic spectrum have not been well defined. As phenotypic heterogeneity is common, we aimed to delineate the age-related penetrance and the full phenotypic spectrum of glaucoma in FOXC1 or PITX2 carriers recruited through a national disease registry. All coding exons of FOXC1 and PITX2 were directly sequenced and multiplex ligation-dependent probe amplification was performed to detect copy number variation. The cohort included 53 individuals from 24 families with disease-associated FOXC1 or PITX2 variants, including one individual diagnosed with primary congenital glaucoma and five with primary open-angle glaucoma. The overall prevalence of glaucoma was 58.5% and was similar for both genes (53.3% for FOXC1 vs 60.9% for PITX2, P=0.59), however, the median age at glaucoma diagnosis was significantly lower in FOXC1 (6.0±13.0 years) compared with PITX2 carriers (18.0±10.6 years, P=0.04). The penetrance at 10 years old was significantly lower in PITX2 than FOXC1 carriers (13.0% vs 42.9%, P=0.03) but became comparable at 25 years old (71.4% vs 57.7%, P=0.38). These findings have important implications for the genetic counselling of families affected by Axenfeld-Rieger syndrome, and also suggest that FOXC1 and PITX2 contribute to the genetic architecture of primary glaucoma subtypes.Emmanuelle Souzeau, Owen M Siggs, Tiger Zhou, Anna Galanopoulos, Trevor Hodson, Deepa Taranath, Richard A Mills, John Landers, John Pater, James E Smith, James E Elder, Julian L Rait, Paul Giles, Vivek Phakey, Sandra E Staffieri, Lisa S Kearns, Andrew Dubowsky, David A Mackey, Alex W Hewitt, Jonathan B Ruddle, Kathryn P Burdon and Jamie E Crai